(1) Field of the Invention
The present invention generally relates to sandwich structures having relatively high strength to weight ratios. More particularly this invention relates to sandwich structures having truss cores and methods for making the same.
(2) Background Information
Structures including solid sheet and/or plate members are ubiquitous, being found in automobiles, buildings, aircraft, industrial equipment, and a host of other applications. Sheet and plate materials are advantageously quite strong and relatively inexpensive. Disadvantageously they tend to be heavy, and therefore generally have a relatively low strength to weight ratio.
Sandwich structures are frequently used in applications and implementations where it is desirable for structures to have a relatively high strength to weight ratio and/or where weight reduction is a significant factor. One example application is as a structural material used in the aerospace industry. One common sandwich structure, typically referred to as a honeycomb structure, includes thin face sheet laminates and a honeycomb core. Honeycomb structures are generally characterized by having a significantly higher strength to weight ratio than sheet or plate materials, especially to bending and buckling loads. Disadvantageously, honeycomb structures tend to be limited to relatively thin face sheets. Further, honeycomb structures tend to be expensive and difficult to manufacture, with the manufacturing process typically including complicated bonding procedures for attaching the honeycomb core to the face sheets.
Another relatively common sandwich structure, referred to as a truss core sandwich panel, includes a corrugated sheet or a truss core disposed between two face sheets. Truss core sandwich panels are also generally characterized as having a significantly higher strength to weight ratio than solid sheet or plate materials, although generally not as high as that of honeycomb structures. Truss core sandwich panels tend to be advantageous for some applications since they may be fabricated with face sheets having a heavier gauge than those of honeycomb structures. However, truss core sandwich panels also tend to be expensive and difficult to manufacture, generally requiring batch type processing.
Priluck, in U.S. Pat. Nos. 5,527,590, 5,679,467, and 5,962,150 (hereafter referred to as the Priluck patents) discloses a structural material having a lattice configuration manufactured from a plurality of segments, which are typically welded together in order to fix their position. The lattice is generally configured in the shape of uniformly stacked pyramids in a three-dimensional array. Manufacturing of the structural materials disclosed in the Priluck patents, however, tends to be highly complex. Fabrication of the truss core alone generally requires multiple steps, including injection molding, manual assembly, investment casting, and/or welding. Attachment of solid face sheets generally adds additional manufacturing steps. As a result the material disclosed in the Priluck patents tends to be expensive. Further, the injection molding and investment casting processes limit the application to materials having relatively low melting temperatures.
Therefore there exists a need for improved sandwich structures and/or truss core sandwich panels and an improved method of manufacturing for reducing the difficulties associated therewith and for producing a relatively inexpensive material.
In one aspect, the present invention includes a structural material. The structural material includes two solid face sheets and a truss core, which includes a plurality of discrete, interwoven wires. The truss core is disposed between the face sheets and attached thereto. Each of the plurality of wires includes multiple points of contact with each of the two solid face sheets. In one variation of this aspect, the interwoven wires and faces sheets include metal and are spot-welded to one another.
In another aspect, this invention includes a method for fabricating a structural material. The method includes bending a plurality of wires, fastening the plurality of wires to a first face sheet, and fastening the plurality of wires to a second face sheet. In one variation of this aspect, the method further includes advancing the first face sheet and the second face sheet from a first roll and a second roll, respectively, the advancing being in a longitudinal direction, and advancing the plurality of wires in the longitudinal direction between the first face sheet and the second face sheet.